It is known to mount integrated circuits on circuit boards via items known as “interposers”. The function of an interposer is to provide a signal interface between a silicon (or other semiconductor) die and a feature such as a socket on a circuit board.
A typical interposer includes one or more metal (e.g. copper) layers and one or more plastic layers. The plastic layer or layers may be quite intricate, with numerous fine features.
As part of a typical technique for manufacturing interposers, a stamping process is applied to a substrate. The substrate may be in the shape of a disk that has a lower, relatively thick layer formed of copper, with an upper layer of moldable plastic formed on the copper. A mold having fine features is impressed on the plastic layer by a stamping mechanism. Over the face of the disk, the mold may impress a repeating pattern, and each instance of the pattern may correspond to an individual one of the interposers to be formed from the disk. After other steps subsequent to molding (e.g., etching and/or laser-trimming, trace-line filling, etc.), the disk may be sawn into pieces to free the individual interposer pieces.
During the stamping process, one problem that may be encountered is trapping of air or excess plastic material at various localities of the mold/substrate. Trapped air or excess material may deform features to be impressed on the substrate, thereby reducing the yield of interposer pieces from the substrate disk.
In some cases, to avoid the problem of trapped air, the stamping process may be performed in vacuum. However, this may increase the cost or difficulty of performing the stamping process. For example, if the stamping is performed in vacuum, it is not possible to retain the mold on the stamping press head by applying vacuum to the mold through the press head.
It is also known to include channels or the like in the mold pattern to allow excess material and/or air to flow away from localities at which it might otherwise be trapped. The presence of such channels occupies space that could otherwise be used for features of the interposer pieces, and thus increases the scale of the interposer pieces and/or reduces the number of interposer pieces that can be produced from a single substrate disk. Accordingly, use of such channels may increase the cost of manufacturing the interposers.